During wirebonding processes, a leadframe must be held motionless while wires are attached between the small contacts of an integrated circuit and the leads of the leadframe. This typically involves clamping the leadframe between a window clamp and a support or hot plate. The window clamp is pressed against the leadframe, and the pressure keeps the leadframe from moving. Window clamps typically have one or more openings (or windows) that align with the die of the leadframe and through which the die and leads can be accessed during the wirebonding process to attach the wires.
Keeping the leadframe perfectly motionless can be challenging. Small deviations in parallelism between the support, leadframe, and/or window clamp can result in imperfect clamping that may allow the leadframe to move during wirebonding processes. Imperfect clamping can also be caused by a number of other factors such as misalignment of the window clamp and leadframe, misalignment of the window clamp and clamping plate, uneven pressure applied to sides of the window clamp, uneven surfaces, and uneven thickness of the leadframe. Imperfect clamping can lead to wirebonding defects that can reduce yield and impact reliability.